By order of the court, a probation officer makes a thorough investigation—a presentence investigation—into the circumstances of the offense and the offender's criminal background and characteristics. The officer gathers information two ways: by conducting interviews and by reviewing documents. The cornerstone of the investigation is the interview with the defendant, during which the officer inquires about such things as the defendant's family, education, employment, finances, physical and mental health, and alcohol/substance abuse. The officer also conducts a home visit to assess the offender's living conditions, family relationships, and community ties.

The officer also interviews other persons who can provide pertinent information about the defendant (i.e. a spouse, child, parent, employer) and the offense (victims, prosecutor, investigating agent, coconspirators).

The presentence report is a critical part of the sentencing process. It must be accurate and distinguish between information that is verified and unverified and between fact and opinion. The presentence report not only helps the court choose an appropriate sentence, but provides important information to help the Bureau of Prisons choose an institution where the offender will serve the sentence, select prison programs that will help with the offender and make release plans. It also provides the USSC with information useful for monitoring sentencing guidelines application and research. The presentence report also helps the US Probation Officer supervising the offender assess the risk the offender poses and assess the needs of the offender.

The probation officer writing the presentence report makes sentencing recommendations (the amount of a fine/restitution, if any, the amount of time an offender will serve on probation, in prison, or on supervised release). He/she also recommends conditions under which offenders are released to the community. Ultimately, the court will decide the actual sentence.